Effects of maternal serum 25-hydroxyvitamin D concentrations in the first trimester on subsequent pregnancy outcomes in an Australian population.

BACKGROUND Low serum 25-hydroxyvitamin D [25(OH)D] concentrations during pregnancy have been associated with adverse pregnancy outcomes in a few studies but not in other studies. OBJECTIVES We assessed the serum 25(OH)D concentration at 10-14 wk of pregnancy and its association with adverse pregnancy outcomes and examined the predictive accuracy. DESIGN In this nested case-control study, we measured serum 25(OH)D in 5109 women with singleton pregnancies who were attending first-trimester screening in New South Wales, Australia. Multivariate logistic regression was conducted to examine the association between low 25(OH)D concentrations and adverse pregnancy outcomes (small for gestational age, preterm birth, preeclampsia, gestational diabetes, miscarriage, and stillbirth). The predictive accuracy of models was assessed. RESULTS The median (IQR) 25(OH)D concentration for the total population was 56.4 nmol/L (43.3-69.8 nmol/L). Serum 25(OH)D concentrations showed significant variation by parity, smoking, weight, season of sampling, country of birth, and socioeconomic status. After adjustment for maternal and clinical risk factors, low 25(OH)D concentrations were not associated with most adverse pregnancy outcomes. The area under the receiver operating characteristic curve (AUC) and likelihood ratio for a composite of severe adverse pregnancy outcomes of 25(OH)D concentrations <25 nmol/L were 0.51 and 1.44, respectively, and, for risk factors alone, were 0.64 and 2.87, respectively. The addition of 25(OH)D information to maternal and clinical risk factors did not improve the ability to predict severe adverse pregnancy outcomes (AUC: 0.64; likelihood ratio: 2.32; P = 0.39). CONCLUSION Low 25(OH)D serum concentrations in the first trimester of pregnancy are not associated with adverse pregnancy outcomes and do not predict complications any better than routinely assessed clinical and maternal risk-factor information.